Driving is a skill that requires your full attention to safely control your vehicle and respond to events happening on the roads around you. Drivers who are distracted or tired can be dangerous not only to the safety of themselves, but also to others on the road, since they are often the cause of severe traffic accidents resulting in human life and property losses. Therefore, there are more and more electronic safety devices being developed and applied in automobiles that are to be used for assisting drivers to drive safely.
Due to their inexperience in wheel steering, obstacle observation and avoidance, parking trajectory estimation and parking space determination, parking can be in general one of the most troublesome problems for those novices and unskilled drivers. It is common for they to make mistakes during parking and that may sometimes leads to real damage and costly repair. Nevertheless, even for those most experienced drivers, trying to park a car into a parking space at an unfamiliar location may be a stressful job. Overall, parking is a critical test for driver's driving skill, especially in a crowded urban area. In addition to the ability for judging whether or not the size of the space is appropriate for the car, it is not until a driver is able to master the skill of wheel steering and also have experience in vehicle dynamic control response that he/she can park a car properly. Those who are not experienced may steer the wheel back and forth for as many times as possible and still can not perform a parking operation correctly.
From the above description, it is known that parking is a task of a high degree of difficulty that not only a driver should have good eyesight and keen observation with regard to parking space evaluation and obstacle avoidance, he also should be able to plan a good parking trajectory while steering. In general, there are three key actions must be performed well in a parking operation, which are:                (1) parking space evaluation;        (2) blind spot and obstacle determination; and        (3) relationship between the sequence of the steering wheel control and the result vehicle dynamic control response.        
Thus, to park a car will require its driver to perform a sequence of actions of perception, decision and motion control. Consequently, to enhance the driver's perception, to perfect the driver's decision and to assist the driver's motion control for reducing invalid operation in steering are the three key issues when it comes design a good parking assistant system. According to a poll released by Japan Automobile Federation, a significant number of common Japanese drivers have a negative impression of parallel and garage parking, which are usually to be ranked in the top-three most troublesome problems in parking.
In response, a wide range of different parking-support systems have been developed. One of which is a parking assistant device, disclosed in TW Pat. No. I229645, which includes: an imaging unit; a monitor arranged at a location near the driver seat of a car; a yawing angle inspection unit; a guidance unit; and a controller. The driver using the aforesaid parking assistant device is able to park a car into a target parking space according to the guidance information provided by the device. However, the aforesaid parking assistant device is disadvantageous in that: it can not automatically judging whether or not the size of the space is appropriate for the car; it only is able to perform an ambient environment perception operation by the detection of its imaging unit; and manual control is still required as when the car is being park and is in reverse, the device will only display parking information such as parking assistance lines on its monitor without providing automatic steering assistance.
Therefore, it is in need of a parking guidance device for a car, capable of using the detection of its image detector and distance detector to obtain a parking information and thus generate a parking track accordingly while directing the car to move autonomously in a moving track conforming to the parking track by controlling the wheel, engine and braking system of the car.